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Photochemical processes on Titan
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  1. Photochemical processes on Titan A Revision from Cassini Observations Cheng Li1, X. Zhang1, J. A. Kammer1, M. C. Liang2, Y. L. Yung1 1California Institute of Technology 2Research Center for Environmental Changes, Academia Sinica, Taiwan

  2. Photochemistry on Titan C2H2, C2H4,C2H6 C2H,C2H3,… N2+,N,N+ C3Hx, C4Hx,… CH,1CH2,3CH2 CH3 e- CH4 N2 surface

  3. The simplest 1D photochemical model Chemical production Chemical loss Vertical transport Mixing ratio Number density Eddy diffusivity

  4. CIRS limb view and FUV stellar occultation C2H2 C2H4 C2H6 Altitude (km) CH4 CH3CCH C3H8 C4H2 C6H6 Mixing ratio Vinatier et al., 2009; Kammer et al., 2011

  5. Retrieval algorithm Ar 1000 altitude C2H2 Mixing ratio Levenberg–Marquardt

  6. Molecular diffusivity Initial guess Retrieved eddy diffusivity

  7. Vinatier et al., 2009; Kammer et al., 2011; Yelle et al., 2008 model 1 model 2 Altitude (km) C2H2 C2H4 C2H6 CH4 CH3CCH C3H8 C6H6 C4H2 Mixing ratio

  8. Haze formation process revealed by the eddy diffusivity Liang et al., 2007 Stabilization due to haze heating Aerosol growth heating Detached haze layer

  9. Conclusion Retrieved eddy diffusivity

  10. How to estimate the sensitivity to chemical rate constants?

  11. Mixing tracer S

  12. How to estimate the eddy diffusivity? Eddy diffusivity Molecular diffusivity adiabats Fulchignoni et al., 2005

  13. Eddy diffusivity adiabats Altitude(km) Eddy diffusivity (cm2/s)

  14. Previous work -- mixing ratio v.s. altitude(km) Lavvas et al, 07 Krasnopolsky, 09

  15. Fractional change of C2H4 by doubling rate constants CH3  1CH2+H 2CH3 + M  C2H6 + M Altitude (km) H + C2H2 + M  C2H3 + M H + C2H4 + M  C2H5 +M

  16. New reaction rate constants (solid lines) H + C2H4 + M  C2H5 + M 604K / 511K / 400K / 285K / 170K (Titan) Moses et al.,2000 This work Lightfoot et al., 1987